Neurofibromatosis type 2 (NF2) is an autosomal, dominantly inherited disorder characterized by multiple tumors of the central nervous system, predominantly bilateral vestibular schwannomas (acoustic neuromas) of the eighth cranial nerve. Other disease features include cranial meningiomas, spinal nerve root schwannomas and presenile lens opacities (Martuza et al. (1988) N. Engl. J. Med. 318:684-688; Kaiser-Kupfer et al. (1989) Arch. Ophthalmol. 107:541-544; Eldridge et al. (1991) Am. J. Hum. Genet. 49:133 (A676)).
The gene for NF2 has been mapped in the chromosomal region 22q12 between the loci D22S1 and D22S28. Experimenters have suggested that the gene acts as a tumor suppressor and that loss or inactivation of the gene therefore results in tumorigenesis (Seizinger et al. (1986) Nature 322:644-647; Seizinger et al. (1987) Science 236:317-319; Rouleau et al. (1987) Nature 329:246-248; Seizinger et al. (1987) Proc. Natl. Acad. Sci. USA 84:5419-5423; Wertelecki et al. (1988) N. Engl. J. Med. 319:278-283; Rouleau et al. (1990) Am. J. Hum. Genet. 46:323-328; Fontaine et al. (1991) Genomics 10:280-283; Wolff et al. (1992) Am. J. Hum. Genet. 51:478-485).
Recently, a candidate human NF2 gene was cloned and identified using physical mapping and positional cloning studies (Trofatter et al. (1993) Cell 72:791-800; Rouleau et al. (1993) Nature 363:515-521). Nonoverlapping DNA deletions in the NF2 gene region from three independent NF2 families and in mRNA from a meningioma in an unrelated NF2 patient, were demonstrated (Trofatter et al., supra). Germ-line and somatic mutations were also shown in DNA of the candidate human NF2 gene from both NF2 patients and NF2-related tumors, including sporadic meningiomas and vestibular schwannomas (Rouleau et al. (1993), supra).
The above-described NF2 gene, originally reported to encode a 587 amino acid protein, is now known to code for a protein having 595 amino acids, called merlin (for moesin-ezrin-radixin like protein). (The corrected NF2 cDNA sequence has been assigned GenBank Accession no. L11353). As evident by its name, the merlin protein exhibits significant homology to the moesin, ezrin and radixin proteins which are highly conserved. These proteins appear to be mediators between plasma membrane proteins and components of the cytoskeleton which regulate cell surface structure and dynamics, as well as cytoplasmic responses to growth factors and other external stimuli (Trofatter et al. supra; Rouleau et al. supra; Luna et al. (1992) Science 258:955-964). Among the family members, merlin shows the most extensive homology (65%) to moesin, ezrin and radixin within a region that spans approximately 340 residues at the N-terminus of the predicted protein (Trofatter et al. supra; Rouleau et al. (1993), supra). Cloning of the candidate NF2 gene was independently confirmed by Rouleau et al., who named the NF2-encoded gene product schwannomin (Rouleau et al. (1993), supra).
The NF2 gene is expressed in multiple tissues (Trofatter et al. supra), suggesting that alterations in this gene might be involved in the development of multiple tumor types in addition to the brain neoplasms typically associated with the inherited disorder. In this regard, cytogenetic and molecular studies have implicated losses in chromosome 22q in several human neoplasms (Seizinger et al. (1991) Cytogenet. Cell Genet. 58:1080-1096), including breast and colon carcinomas, glioblastomas, meningiomas, pheochromocytomas and schwannomas. This indicates that the NF2 gene may constitute a tumor suppressor gene of more general importance in tumorigenesis.
One of the methods by which varient gene products are produced is alternative splicing, a process whereby multiple transcripts are produced from a single gene. These transcript isoforms encode variant proteins with differing functions. In particular, the process yields distinct mRNAs which are often tissue-specific. Thus, the same gene can encode several proteins with differing functions, in a tissue-specific manner. In this regard, it has been suggested that alternative splicing in the C-terminal region of erythrocyte protein 4.1, a member of the moesin family, may be critical for its binding to the cytoskeletal protein, spectrin, and for the mechanical integrity of the red cell membrane (Discher et al. (1993) J. Biol. Chem. 268:7186-7195). However, such transcript isoforms have not heretofore been identified for the NF2 gene.